Storage library systems are often used by enterprises and the like to efficiently store and retrieve data from storage media. In the case of some storage libraries, the media are data cartridges (e.g., tape cartridges) that are typically stored and indexed within a set of magazines. When particular data is requested, a specialized robotic mechanism finds the appropriate cartridge, removes the cartridge from its magazine, and carries the cartridge to a drive that is designed to receive the cartridge and read its contents. Some storage libraries have multiple drives that can operate concurrently to perform input/output (IO) operations on multiple cartridges.
In some implementations, the robotic mechanism is disposed on a carriage that hangs on a system of cables or other supports. The vertical motion of the robotic mechanism can be controlled using gears, pulleys, and the like to move the carriage. Effectively, the carriage acts as a mass, supported against gravity by a vertical drive assembly. If the vertical drive assembly fails (e.g., if there is power loss to the drive assembly), it may be desirable to limit the speed at which the vertical position of the carriage can change (e.g., limit the speed at which the carriage will fall and/or prevent the carriage from moving at all). In this and similar types of environments, various mechanical techniques may typically be used to slow the motion of the mass. Some typical approaches include braking mechanisms, ratcheting mechanisms, and/or other mechanical friction-inducing components. Other typical approaches use liquids or other substances of particular viscosity or compressibility to slow the motion of the mass.
These traditional approaches can be limited in various ways. One such limitation is that mechanical friction-inducing components are likely to generate wear over time and can even produce debris. Another such limitation is that, when using techniques based on physical friction, it is often difficult to control the amount of friction being applied, and the amount of friction force applied often changes over the life of the components (e.g., as they wear). Yet another limitation is that typical friction-inducing components can often be relatively expensive.